Process for developing interwell communication in a tar sand

ABSTRACT

Bituminous sand is contacted with ozone to render the bitumen partly water soluble and to create surface active agents in situ which promote oil-in-water emulsification and increase the water wetability of the sand. Bitumen can then be removed and recovered from the sand formation by flushing it with an aqueous solution.

United States Patent n 1 Redford [111- 3,825,066 [451 July 23,1974

[75] Inventor:

I PROCESS FOR DEVELOPING INTERWELL COMMUNICATION IN A TAR SAND David Arthur Redford, Fort Saskatchewan, Alberta, Canada [73] Assignee: Petrofina Canada Ltd., Calgary,

Canada [22] Filed: July 31, 1972 [21] Appl. No.: 276,732

Related US. Application Data [63] Continuation-impart of Ser. No. 79,346, Aug. 10,

1970, Pat. N0. 3,706,341.

6/1953 Smith et al..' 166/261 2,734,579 2/1956 Elkins 166/261 X 2,914,309 11/1959 Salomonsson 166/256 X 2,973,813 3/1961 Parker 166/261 X 3,044,543 7/1962 Ramey, .lr..... 166/261 X 3,139,928 7/1964 Broussard 166/261 3,205,944 I 9/1965 Walton 166/261 6/1971 Parker [66/261 Primary Examiner-Stephen J. Novosad Attorney, Agent, or FirmErnest Peter Johnson [57] ABSTRACT Bituminous sand is contacted with ozone to render the bitumen partly water soluble and to create surface active agents in situ which promote oil-in-water emulsification and increase the water wetability of the sand.

Bitumen can then be removed and recovered from the sand formation by flushing it with an aqueous solution.

3 Claims, No Drawings PROCESS FOR DEVELOPING INTERWELL COMMUNICATION IN A TAR SAND CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of my application Ser. No. 79,346, filed Aug. 10, 1970 now U.S. Pat. No. 3,706,341.

BACKGROUND OF THE INVENTION This inventionrelates to oxidizing bitumen present in tar sand to render the bitumen water-soluable and more suceptible to oil in water feet so that it can be separated from the sand and recovered.

Large portions of the Athabasca tar sanddeposit in Canada are buried beneath overburden, which can be as much as a thousand'fet in thickness. Because of the over-burden, the bitumen must be separated in situ from the sand if one is to recover the bitumen for oil production on a commercial scale. A number of in situ techniques are presently beinginvestigated. One such approach involves injecting steam into the formation through an injection well. The steam renders the bitumen less viscous and it formsan oil-in-water emulsion with the steam condensate. This emulsion can be forced by a pressure gradient to migrate to a nearby production well, from'which it is recovered. I

A problem associated with the aforementioned steam injection process is that of successfully providing through the tarsand formation a permeable, competent communications path or zone connectingthe injection and production wells. This path, when developed, functions to provide a means for introducing the steam into the formation across a broad area-on a continuous basisand for simultaneously removing the emulsion which is formed. In the past, the path has been developed by: l hydraulically fracturing the for-' Aug. 24,' 1970, now abandoned, I disclose a low-- pressure method for developing a hot, competent, permeable communications path connecting the wells, before pure steam is introduced to the formation. This method comprises introducing an aqueous solution at formation temperature and containing sodium hydroxide (in amount less than 1.0 percent by weight) and a non-ionic surfactant (e.g., between 0.1 and 5 percent by weight of an octylphenoxy polyethylene oxyethanol in which the octyl group is branched and which contains about 5 moles of ethylene oxide) into the fracture system. The solution slowly emulsifies bitumen adjacent to the path. The emulsion is slowly pumped at a relatively low pressure to the production well for re moval. The temperature of the solution is gradually increased at a rate such that all the bitumen entering the flow path is emulsified. As the temperature of the solution is increased, the concentrations of the caustic and surfactant are gradually decreased. Eventually only pure, hot steam is injected. By practising this technique, the danger of vertical fracturing is minimized.

SUMMARY OF THE INVENTION The present invention is concerned with improving the technique of developing an interwell communications path, prior to injecting steam only. More specifically, I have found that, when bituminous sand is contacted with ozone and is subsequently flushed with water or-an aqueous solution containing caustic and a non-ionic surfactant, some bitumen separatesfrom the sand and is carried away with the flushing solution, thereby gradually developing a permeable communications path through the formation. Without wishing to be bound by any technical explanation of this process, I believe that the ozone oxidizes bitumen to form acidic groups; the product is characterized by decreased bitumen-water interfacial tension, increased wetability of the sand, increased solubility of the bitumen in water and increased ease of oil-in-wateremulsion formation. If a'caustic solution is used to flush the formation, I believe the caustic reacts with acidic groups in the bitumen to form organic salts which increase the hydrophilic character of the bitumen, thus rendering an increased amount water soluble and. a further fraction surface active which aids the bitumen to combine and move with the water.

According to one embodiment of the invention, the methodcomprises: (l) injecting ozone into tar sand to contact bitumen and react with it to form a product which is relatively water soluble in comparison to unreacted-bitumen; and (2) flushing the tar sand with a so-' lution which separatesand removes reacted bitumen from the sand This solution may be water, water containing caustic, or water containing caustic and a non-ionic surfactant.

DESCRIPTION OF THE PREFERRED EMBODIMENT The following examples illustrate the invention: Example I This example illustrates the use of ozone as a means Y for establishing a bitumen-depleted zone within tar sand.

A 1 /2 X 18 inch glass column was packed with 800 grams of Athabasca tar sand. Oxygen containing 6 7 percent by volumn ozone was passed through the tube for 2 days at millimetres per minute. The experiment was carried out at roomtemperature.

During this period, the colour of the sample changed from black to gray as many white, clear sand grains appeared.

At the end of the two day period, the columnwas eluted with water. The collected eluent was dark brown in colour and foamed when shaken lightly. It was evap- A portion of the water-extracted ozonized tar sand- Rohm and Haas). Within 30 minutes the solution turned dark brown, indicating very rapid emulsification of the bitumen.

Part B was saturated at 40 with'water containing 0.2 percent by weight sodium hydroxide. No change in the colour of the solution had occurred after 2 days.

Part C was saturated at 40 with water containing 0.4 percent by weight Triton X-45. Some darkening of this solution occurred in 30 minutes.

A fourth part D of the ozonized tar sand was-stirred with water at room temperature under a microscope. The sand and bitumen separated and the bitumen formed globules in the water phase. When nonozonized tar sand was subjected to the same test, nothing happened.

From these results it'will be noted that:

a. treatment of tar sand with ozone converts some bitumen to a water-soluble form;

b. some of the ozonized bitumen has surface active characteristics; and

c. ozonized tar sand is more amenable to spontaneous emulsification with an aqueous solution of sodium hydroxide and non-ionic surfactant than is otherwise the case.

Example 11 This example illustrates that ozone is effective at formation temperature. v

A horizontal 3-foot X 2-inch column was tightly packed with 5.2 pounds of Athabascatar sand. A

inch diameter path of 20 40 mesh round sand was incorporated in the tar sand along the bottom of the column.

Oxygen containing 5-6 percent by volunm ozone was passed through the column for.6l hours. The exit gas contained only 1 percent ozone.

A second 50 gram sample was extracted with 1.1 litres of water. The solution required 41.4 cubic centimetres of 0.1 sodium hydroxide to neutralize it. This test indicated the formation of acid groups due to mac tion between the ozone and bitumen.

ln sampling the tube, samples were taken from 4 equal-length sections along the tube, designated A, B, C, and D, starting from the ozone-inlet end. The bitumen was extracted from each of these samples and from a sample of unozonized'tar sand (designated sample 0) using toluene reflux. Elemental analyses of these bitumen samples and their molecular weights are shown in Table 111. Standard S.A.R.A. analyses were conducted on each of the samples; thus dividing'each of them into asphaltenes, resin 1, resin: 11', saturates, and aromatics. The results of this analysis are given in Table IV. Elemental analyses and molecular weights were carried out on each of the sub-samples. The results are shown in Table- V. These analyses show that in general ozonolysis was limited to the asphaltene and resin fractions of the bitumen and that it resulted in a lower mo lecular weight and a decrease in'the sulphur content. The saturates and aromaticswere little affected; these fractions, however, are of low molecular weight and viscosity. Thus ozonolysis is attacking that part of the bitumen which is of highest molecular weight and viscosity, and converting it into water soluble or more bydrophylic material.

TABLE 1V.-Analysis of Unozonized and Partially Ozonized Bitumen I Car- Hy- Oxy- Nitro- 1 v bon drogen gen Sulfur gen Ash Mo- Sa'm perperperpe'rperperlecular ple cent cent cent cent cent cent weight 0, 81.82 10.37 0.78 5.17 1.23. 1448 A 81.63 9.98 2.18 4.02 1.28 1.11- 668 B 81.71 10.62 2.25 3.97 0.88 0.92 625 C 81.66 10.6.7 2.37 3.95 0.71 634 D 81.44 10.55 2.25 4.30 1.05 1.05 641 TABLE V.S.A. R.A. Analysis of Unozonized and Partially A SO-gram sample of the ozonized tar sand was ex- Asphal- R I l R u Sattu- Aroenes esrns esrns l'a CS matics tracted wrthSOO m llilitres of water to yield adark Sample percent percent percent percent percent brown solution WhlCh foamed when shaken lightly. Evaporation of the solutlon to dryness ylelded 0.237 g v21-3 -3 grams of solid material. Thrsmater al analyzed as fol- B 2: if 12:: lows: c 25.8 39.5 2.5 20.0 9. D 24.5 44.8 2.6 18.7 6. Table 11 .componem %b weight TABLE Vl.-Ana1ysis of Unozonized and Partially Ozonized- Bitumen After S.A.R.A. Analysis carbon 28.7 Cary-' xyrtrohydrogen 3.7 5 5 bun drogen gen Sulfur gen Ash Mooxygen 5 1.3 Samperperperperperperlecular nitrogen 1.3 ple cent cent cent cent cent cent weight sulphur 8.2 drying loss 6.8 A h l 3 O 78.84 7:83 3.03 8.48 1.34 0.64 4797 This surface tension of a solution of this material m A 4J1 Q79 4, water was as follows. B 76.86 7.74 4.88 7.68 0.82 1.88 C 76.87 7.65 4.90 7.75 0.90 1.80 D 77.38 7.88 4.44 7.71 0.89 1.53 3493 Resins 1': TABLE "I O 76.89 9.72 3.97 5.48 0.73 1.01 727 r A 77.27 9.48 4.23 4.77 0.77 1.31 731 cpnccmmtion Surface tension B 78.53 9.73 6,05; 4.65 0.25 563 'p.p.m. Pynes/cm. 5 C 78.71 9.63 6.05 4.71 0.26 590 D 78.67 9.73 5.97 4.64 0.17 617 250 69.6 Resins l1: 500 62.5 0 76.31 9.44 4.44 2.30 0:30 1000 60 A 77.47 9.89 6.03 1.17 1.17 a 2000 53.7 B 78.99 10.50 7.85 1.96 0.18 1. .1. 9- 3 9. L62.

TABLE Vl-fiMYii of Unozonized and Partially. Ozonized A Bitumen After S.A.R.A. Analysis-Continued i percent NaOH was pggsed through the Cell for days M; (20'cc/hour). An addmonal 8.7 percent of the b1tumen hon drogcn gen Sulfur gen Ash M nin the cell was removed during this period. Most of the Smn- M W P"- cell effluent which was collected during the first 6 da 5 t 1 hr y can can 5 of water in ection was neutrahzed to pl-i7, and th1s ma- D 79.17 [Q63 8.00 1.7] 0.19 was e y d through the cell six i es pro ti e 8: 13.31 0.17 0.28 0.45 454 cedure removed a further 2 percent of the bitumen A 85:92 13.34 0.14 0.27 41 433 from the cell, for a total bitumen recovery of 20.2 per- 8 32-2,, 13%: g-gg 8%: :3 1: g3; 10 cent. When the cell was opened and the tar sands ex- D 86:28 13:10 0115 0:25 .13 412 i amined it became evident that the whole cross section 0 0 Aromatics: E of the tube had been affected to some extent by the 0. r I B -3 1 1 -4 33 -NaOH-solut1on flush, and neutrahzed-effluent recycle, 0 85.30 10.45 0.48 0.16 areas n tab n h mi nd ath D 85.29 10.48 0.50 3.22 0.26 379 but 50m: 0 Y ea e g a1 Sa P and extending around the glass surface, the bitumen had been extensively removed.

bitumen at formation temperatures (40 F) to form Example water-soluble highly-oxygenated materials which have A second 3-foot by 2-inch horizontal tube was packed as bat-Ore and ozone (6 percent in 02) was surface actrve properties in both acld form and as neupassed through for 7 days (80 percent of the ozone was walled Salts Passmg ofiwaler through an ozomzed still being absorbed by the cell after 7 days). Distilled I 9 tar sands results water (20 ml/hr) and ozone (6 percent in 0,) were then tumen m this removal ls-extenswe m passed through the tube for 6 days. Examination of the other areas It Is mmor' when percent Sodium hycell disclosed areas around the sand path and extending out around the surface of the 'cell which had been largely depleted of bitumen, leaving clean. white sand.

The initial effluent from the cell (first days effluent after commencing water injection) was an amber color (pH, 1.35) and contained about 6 percent watersoluble organic material. The surface tension of this material as a function of concentration together with the surface tension of this material after neutralization tumen is removed and the highly-depleted areas are extended. Recycling the cell effluents, which contain surfurther bitumen removal.

What is claimed is:

tained in a tar sand formation to convert the bitumen to a partly water-soluble state, which comprises:

397 combination of ozonolysis, distilled-water flush,

These'results indicate that ozone readily reacts with droxide solution is passed through such a bed, more bi-' face active agents which were formed insitu, results in 1. A method for in situ treatment of bitumen conwith NaOH is Shown in Table contacting bitumen 1n the formatlon w1th ozone e whereby the bitumen and ozone react to form a TABLE V" product having greater water solubility than nonreacted bitumem "W" m g Concentration Surface Tension Surface Tension 2. A method for converting bitumen contamed 1n a .E -2.:! NiPlEl QdiQfltl su j m, 40 tar sand formation to a partly water-soluble state and 4000 56 emulsifying the product whereby it may be moved 8000 59 53.5 i A 7 16,000 43 495 through the formation, wh1ch comprises: 53 888 47 1: contacting bitumen in the formation with ozone 321000 5 whereby the bitumen and ozone .react to form a 42,000 45.8 5 product having greater water solubility than nonreacted bitumen; and

contacting the product with water to emulsify it. 3. The method as set forth in claim 2 wherein: the product is contacted with water containing so- 50 dium hydroxide. 1

Approximately 9.5 percent of the bitumen originally I in the cell wasremoved during the 6 days of water injection.

The test cell was reassembled and a solution of 0.2 

2. A method for converting bitumen contained in a tar sand formation to a partly water-soluble state and emulsifying the product whereby it may be moved through the formation, which comprises: contacting bitumen in the formation with ozone whereby the bitumen and ozone react to form a product having greater water solubility than non-reacted bitumen; and contacting the product with water to emulsify it.
 3. The method as set forth in claim 2 wherein: the product is contacted with water containing sodium hydroxide. 